This invention relates to non-pneumatic tires for wheel apparatus such as wheelchairs, and particularly to an endless integrally molded tire for such purposes.
Wheelchair tires have conventionally been produced from hollow cylindrical elastomeric extrusions. The pre-cured extrusion is cut to length, fastened into a circle using a device similar to a hose barb, then machine stretched onto the rim. In a similar technique, a wire is loosely inserted in the hollow axial passage of the extrusion, and the extrusion and internal wire fastened into a circle by twisting or clenching the ends of the wire together, producing a joint at the abutting ends of the extrusion.
The above prior art wheelchair tires have suffered from certain problems. A primary one is the relative ease with which the tire assembly is susceptible to rolling off the rim from side loading encountered when turning the wheelchair sharply. This roll-off tendency is believed attributable at least in part to the joint formed between abutting ends of the extrusion, and the fact that the wire insert has freedom of movement inside the extrusion, and is subject to breaking. Another problem is encountered by the wheelchair user when his wheelchair tire needs replacement. It is generally necessary to have a new tire installed on the wheelchair using special machinery, oftentimes requiring transport of the wheelchair back to the factory or repair center.
In another prior wheelchair tire configuration, an endless extrusion surrounds an embedded or partially embedded coil spring located at the internal diameter of the tire and whose ends are interconnected. The tire may be snapped on and off an associated rim by hand. The coil spring, while aiding mounting and removal of the tire from the rim, will undergo unacceptably high elongation under side loading and therefore resistance to roll-off is less than desired.
It is a primary object of the present invention to provide a snap-on endless integrally molded wheelchair tire which is resistant to roll-off even under elevated side loading forces, and which can be easily replaced in the field.